Wavelength-division-multiplexed passive optical network system using wavelength-seeded light source

Abstract

An economical wavelength-division-multiplexed passive optical network (WDM-PON) system is realized by directly modulating a wavelength-seeded light source to transmit upstream or downstream data, without using an expensive external modulator. A multiplexed signal having the same wavelength as the waveguide grating is generated and used to control the temperature of the waveguide grating and adjust the wavelength of a wavelength-division-multiplexed signal routed to a transfer link. The wavelength selectivity and stabilization of each light source are not required. Since upstream and downstream signals can be multiplexed and demultiplexed concurrently by each waveguide grating located in the central office and the remote node, it is possible to reduce the number of waveguide gratings used in a WDM optical network. In addition, upstream and downstream signals can be transmitted concurrently using a single-strand transfer optical fiber, thereby realizing an economical and efficient WDM-PON.

1 . A wavelength division multiplexed passive optical network system including a central office and a remote node which is linked to the central office and a plurality of subscriber units through optical fibers, wherein said central office includes: 
 a first broadband light source for supplying an optical signal to be injected into a downstream wavelength-seeded light source;    a second broadband light source for supplying an optical signal to be injected into an upstream wavelength-seeded light source included in the plurality of subscriber units;    a 2×2 optical splitter for combining broadband signals generated by the first and second broadband light sources with upstream and downstream optical signals, respectively;    a 1×N mux/demux for spectrum-slicing a broadband signal generated by the first broadband light source and at the same time demultiplexing an upstream optical signal and/or multiplexing a downstream optical signal;    a wavelength-seeded light source for receiving a spectrum-sliced optical signal and outputting a downstream optical signal having the same wavelength as the received optical signal and directly modulated according to downstream data to be transmitted;    an optical receiver for detecting an upstream optical signal as an electric signal; and    a wavelength-division-multiplexer for demultiplexing the upstream optical signal and the spectrum-sliced optical signal and multiplexing the downstream optical signal.    
     
     
         2 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said 1×N mux/demux comprises a 1×N waveguide grating.  
     
     
         3 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said first broadband light source comprises an erbium-doped fiber amplifier.  
     
     
         4 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said first broadband light source comprises a semiconductor optical amplifier.  
     
     
         5 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said first broadband light source comprises a light-emitting diode.  
     
     
         6 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said first broadband light source comprises a superluminescent LED.  
     
     
         7 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said second broadband light source comprises an erbium-doped fiber amplifier.  
     
     
         8 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said second broadband light source comprises a semiconductor optical amplifier.  
     
     
         9 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said second broadband light source comprises a light-emitting diode.  
     
     
         10 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said second broadband light source comprises a superluminescent LED.  
     
     
         11 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said downstream wavelength-seeded light source comprises a Fabry-Perot laser.  
     
     
         12 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said downstream wavelength-seeded light source comprises a reflective semiconductor optical amplifier.  
     
     
         13 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said upstream and downstream signals have distinct wavelengths of 1,300 nm and 1,540 nm, or 1,540 nm and 1,300 nm, respectively.  
     
     
         14 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said upstream and downstream signals have distinct wavelengths of 1,300 nm and 1,580 nm, or 1,580 nm and 1,300 nm, respectively.  
     
     
         15 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said upstream and downstream signals have distinct wavelengths of 1,540 nm and 1,580 nm, or 1,580 nm and 1,540 nm, respectively.  
     
     
         16 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said remote node includes a 1×N mux/demux for spectrum-slicing a broadband signal generated and transmitted from the central office and at the same time demultiplexing a multiplexed downstream optical signal transmitted from the central office, while multiplexing an upstream optical signal transmitted from the subscriber units.  
     
     
         17 . The wavelength division multiplexed passive optical network system according to  claim 16 , wherein said 1×N mux/demux comprises a waveguide grating.  
     
     
         18 . The wavelength division multiplexed passive optical network system according to  claim 1 , wherein said subscriber units include: 
 a wavelength-division-multiplexer for demultiplexing the downstream optical signal and an optical signal spectrum-sliced at and transmitted from the remote node and for multiplexing the upstream optical signal;    an optical receiver for receiving the downstream optical signal; and    an upstream wavelength-seeded light source for receiving the optical signal spectrum-sliced at the remote node and outputting an upstream optical signal having the same wavelength as the received optical signal spectrum-sliced at the remote node and directly modulated according to upstream data to be transmitted.    
     
     
         19 . A wavelength division multiplexed passive optical network system including a central office and a remote node which is linked to the central office and a plurality of subscriber units through optical fibers, wherein said central office includes: 
 a first broadband light source for supplying an optical signal to be injected into a downstream wavelength-seeded light source;    a second broadband light source for supplying an optical signal to be injected into an upstream wavelength-seeded light source included in the plurality of subscriber units;    an N×N mux/demux for spectrum-slicing a broadband signal generated by the first broadband light source and at the same time demultiplexing a multiplexed upstream optical signal from the remote node and/or multiplexing a downstream optical signal;    a first optical circulator for inputting a broadband signal generated by the first broadband light source to the N×N mux/demux and a multiplexed downstream optical signal outputted from the N×N mux/demux to a transfer optical fiber;    a second optical circulator for inputting a broadband signal generated by the second broadband light source to the transfer optical fiber and a multiplexed upstream optical signal transmitted to the N×N mux/demux for said demultiplexing;    a wavelength-division-multiplexer for demultiplexing the multiplexed downstream optical signal inputted from the first optical circulator, the broadband signal inputted from the second optical circulator and said multiplexed upstream optical signal;    a wavelength-seeded light source for receiving the spectrum-sliced optical signal and outputting a downstream optical signal having the same wavelength as the received optical signal and directly modulated according to downstream data to be transmitted; and    an optical receiver for detecting an upstream optical signal as an electric signal.    
     
     
         20 . The wavelength division multiplexed passive optical network system according to  claim 19 , wherein said remote node includes an 1×N mux/demux for spectrum-slicing a broadband signal generated and transmitted from the central office and at the same time demultiplexing a multiplexed downstream optical signal transmitted from the central office, while multiplexing an upstream optical signal transmitted from the subscriber units.  
     
     
         21 . The wavelength division multiplexed passive optical network system according to  claim 19 , wherein said subscriber units include: 
 a wavelength-division-multiplexer for demultiplexing the downstream optical signal and an optical signal spectrum-sliced at and transmitted from the remote node and multiplexing the upstream optical signal;    an optical receiver for receiving the downstream optical signal; and    an upstream wavelength-seeded light source for receiving the optical signal spectrum-sliced at the remote node and outputting an upstream optical signal having the same wavelength as the received optical signal spectrum-sliced at the remote node and directly modulated according to upstream data to be transmitted.    
     
     
         22 . A wavelength division multiplexed passive optical network system including a central office and a remote node which is linked to the central office and a plurality of subscriber units through optical fibers, wherein said central office includes: 
 a broadband light source for simultaneously supplying optical signals to be injected into a downstream wavelength-seeded light source and an upstream wavelength-seeded light source;    a fiber Bragg grating for passing a portion of broadband optical signals generated by the broadband light source, said portion having a wavelength of a downstream optical signal, while said grating reflects a portion having a wavelength of an upstream optical signal;    an optical circulator for outputting the broadband signals generated by the broadband light source to the fiber Bragg grating, said multiplexed downstream optical signal to a transfer optical fiber and said multiplexed upstream optical signal to an N×N mux/demux;    said N×N mux/demux for receiving and spectrum-slicing a broadband signal having the same wavelength as the downstream optical signal passing through the fiber Bragg grating and at the same time multiplexing a downstream optical signal and/or demultiplexing an upstream optical signal;    a wavelength-seeded light source for receiving the spectrum-sliced optical signal and outputting the downstream optical signal to be multiplexed, said downstream optical signal to be multiplexed having the same wavelength as the received optical signal and being directly modulated according to downstream data to be transmitted; and    an optical receiver for detecting an upstream optical signal as an electric signal.    
     
     
         23 . The wavelength division multiplexed passive optical network system according to  claim 22 , wherein said remote node includes an 1×N mux/demux for receiving a broadband signal having the same wavelength as the upstream optical signal reflected by and transmitted from the fiber Bragg grating and spectrum-slicing the received broadband signal and at the same time demultiplexing a multiplexed downstream optical signal transmitted from the central office, while multiplexing an upstream optical signal transmitted from the subscriber units.  
     
     
         24 . The wavelength division multiplexed passive optical network system according to  claim 22 , wherein said subscriber units include: 
 a wavelength-division-multiplexer for demultiplexing a downstream optical signal and for demultiplexing and multiplexing a spectrum-sliced optical signal transmitted from the remote node and an upstream optical signal;    an optical receiver for receiving a downstream optical signal; and    an upstream wavelength-seeded light source for receiving the spectrum-sliced optical signal and outputting an upstream optical signal having the same wavelength as the received spectrum-sliced optical signal and directly modulated according to upstream data to be transmitted.